做一个用户中奖记录页面,展示每条记录和总金额,遇到浮点数相加出现问题。
Js的浮点数在比较或者做运算的时候会不准确,这个只在初学js的时候读到过概念性的东西,这次就遇到了就在这里记一笔,做一下相关拓展,网上处理的方法也很多,这里摘要一些博主的。
浮点数运算:
转自:https://blog.csdn.net/u013347241/article/details/79210840
思路是将小数转成整数来运算,之后再转回小数。
'use strict' var accAdd = function(num1, num2) { num1 = Number(num1); num2 = Number(num2); var dec1, dec2, times; try { dec1 = countDecimals(num1)+1; } catch (e) { dec1 = 0; } try { dec2 = countDecimals(num2)+1; } catch (e) { dec2 = 0; } times = Math.pow(10, Math.max(dec1, dec2)); // var result = (num1 * times + num2 * times) / times; var result = (accMul(num1, times) + accMul(num2, times)) / times; return getCorrectResult("add", num1, num2, result); // return result; }; var accSub = function(num1, num2) { num1 = Number(num1); num2 = Number(num2); var dec1, dec2, times; try { dec1 = countDecimals(num1)+1; } catch (e) { dec1 = 0; } try { dec2 = countDecimals(num2)+1; } catch (e) { dec2 = 0; } times = Math.pow(10, Math.max(dec1, dec2)); // var result = Number(((num1 * times - num2 * times) / times); var result = Number((accMul(num1, times) - accMul(num2, times)) / times); return getCorrectResult("sub", num1, num2, result); // return result; }; var accDiv = function(num1, num2) { num1 = Number(num1); num2 = Number(num2); var t1 = 0, t2 = 0, dec1, dec2; try { t1 = countDecimals(num1); } catch (e) { } try { t2 = countDecimals(num2); } catch (e) { } dec1 = convertToInt(num1); dec2 = convertToInt(num2); var result = accMul((dec1 / dec2), Math.pow(10, t2 - t1)); return getCorrectResult("div", num1, num2, result); // return result; }; var accMul = function(num1, num2) { num1 = Number(num1); num2 = Number(num2); var times = 0, s1 = num1.toString(), s2 = num2.toString(); try { times += countDecimals(s1); } catch (e) { } try { times += countDecimals(s2); } catch (e) { } var result = convertToInt(s1) * convertToInt(s2) / Math.pow(10, times); return getCorrectResult("mul", num1, num2, result); // return result; };
//计算小数位的长度
var countDecimals = function(num) { var len = 0; try { num = Number(num); var str = num.toString().toUpperCase(); if (str.split('E').length === 2) { // scientific notation var isDecimal = false; if (str.split('.').length === 2) { str = str.split('.')[1]; if (parseInt(str.split('E')[0]) !== 0) { isDecimal = true; } } let x = str.split('E'); if (isDecimal) { len = x[0].length; } len -= parseInt(x[1]); } else if (str.split('.').length === 2) { // decimal if (parseInt(str.split('.')[1]) !== 0) { len = str.split('.')[1].length; } } } catch(e) { throw e; } finally { if (isNaN(len) || len < 0) { len = 0; } return len; } }; //将小数转成整数 var convertToInt = function(num) { num = Number(num); var newNum = num; var times = countDecimals(num); var temp_num = num.toString().toUpperCase(); if (temp_num.split('E').length === 2) { newNum = Math.round(num * Math.pow(10, times)); } else { newNum = Number(temp_num.replace(".", "")); } return newNum; }; //确认我们的计算结果无误,以防万一 var getCorrectResult = function(type, num1, num2, result) { var temp_result = 0; switch (type) { case "add": temp_result = num1 + num2; break; case "sub": temp_result = num1 - num2; break; case "div": temp_result = num1 / num2; break; case "mul": temp_result = num1 * num2; break; } if (Math.abs(result - temp_result) > 1) { return temp_result; } return result; };
对金额的处理:
转自: https://www.css88.com/archives/7324
格式化金额:
/** * 将数值四舍五入(保留2位小数)后格式化成金额形式 * * @param num 数值(Number或者String) * @return 金额格式的字符串,如'1,234,567.45' * @type String */ function formatCurrency(num) { num = num.toString().replace(/$|\,/g,''); if(isNaN(num)) num = "0"; sign = (num == (num = Math.abs(num))); num = Math.floor(num*100+0.50000000001); cents = num%100; num = Math.floor(num/100).toString(); if(cents<10) cents = "0" + cents; for (var i = 0; i < Math.floor((num.length-(1+i))/3); i++) num = num.substring(0,num.length-(4*i+3))+','+ num.substring(num.length-(4*i+3)); return (((sign)?'':'-') + num + '.' + cents); }
或者
function fmoney(s, n) { /* * 参数说明: * s:要格式化的数字 * n:保留几位小数 * */ n = n > 0 && n <= 20 ? n : 2; s = parseFloat((s + "").replace(/[^d.-]/g, "")).toFixed(n) + ""; var l = s.split(".")[0].split("").reverse(), r = s.split(".")[1]; t = ""; for (i = 0; i < l.length; i++) { t += l[i] + ((i + 1) % 3 == 0 && (i + 1) != l.length ? "," : ""); } return t.split("").reverse().join("") + "." + r; } //调用 fmoney(9.7,2);//9.70 fmoney('12345.675910', 3);//12,345.676
不过关系到经济利益的时候,还要考虑舍去或者舍入几厘。大家懂的,每个用户几厘钱可能带来巨大的经济收益。
就比如说收手续费,如果一笔手续费计算出来是 3.4521 元,精确到分一般都会收 3.46 元。当然如果是付出去,那可能就是直接舍去了,一般会计算为 3.45 元。
function number_format(number, decimals, dec_point, thousands_sep,roundtag) { /* * 参数说明: * number:要格式化的数字 * decimals:保留几位小数 * dec_point:小数点符号 * thousands_sep:千分位符号 * roundtag:舍入参数,默认 "ceil" 向上取,"floor"向下取,"round" 四舍五入 * */ number = (number + '').replace(/[^0-9+-Ee.]/g, ''); roundtag = roundtag || "ceil"; //"ceil","floor","round" var n = !isFinite(+number) ? 0 : +number, prec = !isFinite(+decimals) ? 0 : Math.abs(decimals), sep = (typeof thousands_sep === 'undefined') ? ',' : thousands_sep, dec = (typeof dec_point === 'undefined') ? '.' : dec_point, s = '', toFixedFix = function (n, prec) { var k = Math.pow(10, prec); console.log(); return '' + parseFloat(Math[roundtag](parseFloat((n * k).toFixed(prec*2))).toFixed(prec*2)) / k; }; s = (prec ? toFixedFix(n, prec) : '' + Math.round(n)).split('.'); var re = /(-?d+)(d{3})/; while (re.test(s[0])) { s[0] = s[0].replace(re, "$1" + sep + "$2"); } if ((s[1] || '').length < prec) { s[1] = s[1] || ''; s[1] += new Array(prec - s[1].length + 1).join('0'); } return s.join(dec); } console.log(number_format(2, 2, ".", ","))//"2.00" console.log(number_format(3.7, 2, ".", ","))//"3.70" console.log(number_format(3, 0, ".", ",")) //"3" console.log(number_format(9.0312, 2, ".", ","))//"9.03" console.log(number_format(9.00, 2, ".", ","))//"9.00" console.log(number_format(39.715001, 2, ".", ",", "floor")) //"39.71" console.log(number_format(9.7, 2, ".", ","))//"9.70" console.log(number_format(39.7, 2, ".", ","))//"39.70" console.log(number_format(9.70001, 2, ".", ","))//"9.71" console.log(number_format(39.70001, 2, ".", ","))//"39.71" console.log(number_format(9996.03, 2, ".", ","))//"9996.03" console.log(number_format(1.797, 3, ".", ",", "floor"))//"1.797"
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Numeral.js
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accounting.js
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Math.js
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这几个类库帮我们解决很多这类问题,不过通常我们前端做这类运算通常只用于表现层,应用并不是很多。所以很多时候,一个函数能解决的问题不需要引用一个类库来解决。